Top Open Source Projects using Java
A curated collection of the 38 best free and open-source projects built using Java. Discover popular repositories, architecture patterns, and trending software in 2026.
xyd
MITCreate powerful, interactive documentation with hot reloading, TypeScript support, custom components, and built-in API docs generation.
XWiki
LGPL-2.1XWiki is a flexible, feature-rich wiki software that helps organizations structure and share knowledge efficiently.
SeriesGuide
Android app for tracking TV shows and movies you're watching, have watched, or plan to watch, powered by TMDb data.
LibreOffice
GPL-3.0Complete free office suite compatible with Microsoft formats (.doc, .docx, .xls, .xlsx, .ppt, .pptx). Open source alternative with regular updates.
Keycloak
Apache-2.0Comprehensive open source identity management solution offering single sign-on, social login, and fine-grained authorization for applications and services.
Gravitee
Apache-2.0Full-lifecycle API management platform that unifies synchronous and asynchronous ecosystems. Manage APIs, event streams, and AI agents with enterprise security and 4x faster gateway performance.
Firecrawl
AGPL-3.0API for AI agents to search, scrape, crawl, and interact with the live web, returning clean Markdown, structured JSON, or screenshots from any page.
draw.io
Apache-2.0Create professional diagrams online or offline with security-first approach. No registration needed. Works with Google Drive, SharePoint, Atlassian, and more.
ByteChef
NOASSERTIONCreate intelligent automation workflows combining AI agents with your favorite apps and services. Connect, automate, and scale your operations without complex coding.
AutoMQ
Apache-2.0AutoMQ is a serverless Kafka alternative built on S3 that offers 10x cost savings, easy scalability, and full Kafka compatibility.
SuperTokens
NOASSERTIONOpen-source authentication solution offering flexible, self-hosted user management with advanced features and easy integration.
Structr
NOASSERTIONOpen-source low-code platform combining Neo4j graph database, visual schema editor, automatic REST APIs, and page rendering in one self-hosted environment.
Standard Notes
AGPL-3.0Cross-platform note-taking app with end-to-end encryption, offline access, and powerful organization features for privacy-conscious users.
Signal
AGPL-3.0Secure messaging app with state-of-the-art encryption, voice/video calls, group chats, and file sharing. No ads, trackers, or data collection.
Scalar
MITScalar is an open-source tool for building, customizing, and hosting interactive API documentation with OpenAPI support.
QuestDB
Apache-2.0Open-source time-series database offering massive ingestion throughput, millisecond queries, and SQL extensions, designed for optimal performance at any hardware scale.
Apache Pinot
Apache-2.0Sub-second SQL queries on fresh streaming data at petabyte scale, built for high-concurrency user-facing apps and AI agent backends.
Peergos
AGPL-3.0A peer-to-peer encrypted filesystem for secure file storage, sharing, and collaboration with end-to-end encryption and user-controlled data.
OSMAnd
NOASSERTIONComprehensive offline navigation app with detailed maps, turn-by-turn guidance, and specialized routing for hiking, cycling, and walking worldwide.
Organic Maps
NOASSERTIONFree, open-source offline maps app with detailed trails, turn-by-turn navigation, and zero tracking. Perfect for hikers, cyclists, and travelers seeking privacy.
OpenSearch
Apache-2.0Community-driven, Apache 2.0-licensed search and analytics suite for ingesting, searching, visualizing, and analyzing data at scale with AI/ML capabilities.
Opengrep
LGPL-2.1Opengrep is a community-driven fork of SemgrepCE, providing accessible static code analysis and security scanning for developers.
Notesnook
GPL-3.0End-to-end encrypted note-taking app with zero-knowledge architecture, cross-device sync, web clipper, and a self-hostable sync server.
LanguageTool
LGPL-2.1Check grammar, punctuation, and spelling errors instantly with AI-powered technology. Supports 30+ languages with browser extensions and desktop apps.
Kestra
Apache-2.0YAML-based orchestration platform with 1400+ plugins for running data pipelines, AI workflows, and infrastructure automation across teams at scale.
Jitsi
Apache-2.0Host encrypted video conferences directly in your browser, deploy on your own servers, or integrate into applications - all with this powerful open source platform.
Apache IoTDB
Apache-2.0Apache IoTDB manages industrial IoT time-series data with high-throughput read/write, edge-cloud sync, ultra-high compression, and integrations with Hadoop, Spark, Flink, and Grafana.
Godot
MITBuild 2D, 3D, and XR games with a full-featured engine that includes its own scripting language, scene editor, and export tools for multiple platforms.
Logstash
NOASSERTIONLogstash is a free and open server-side data processing pipeline that ingests data from multiple sources, transforms it, and sends it to your desired destination.
Apache Druid
Apache-2.0Columnar, time-indexed analytics database built for streaming and batch data at scale, handling billions to trillions of rows with millisecond query response times.
DBeaver
Apache-2.0Cross-platform database management tool for exploring, editing, and querying SQL databases including MySQL, PostgreSQL, SQLite, MariaDB, and more.
CrateDB
Apache-2.0Distributed SQL database designed for high-speed ingestion and complex queries on massive datasets, ideal for IoT and time-series data.
ClearFlask
Apache-2.0ClearFlask is an open-source platform for collecting, analyzing, and acting on customer feedback to drive product development.
Chat2DB
NOASSERTIONAI-powered SQL client that converts natural language to SQL queries. Supports MySQL, Redis, MongoDB with Text2SQL, BI dashboards, and secure database management.
AppSmith
Apache-2.0Low-code platform for creating powerful internal tools and dashboards with drag-and-drop ease, robust integrations, and customizable workflows.
AITable
AGPL-3.0Visual database and workflow automation tool with AI-powered features and 6,000+ app integrations
Airbyte
NOASSERTIONSeamlessly sync data from any source to any destination with a flexible, extensible platform that grows with your data needs.
Elasticsearch
NOASSERTIONElasticsearch is an open-source, RESTful search engine designed for scalability, reliability, and easy management.
